REMOTE SENSING OF TOTAL COLUMN PERCEPTIBLE WATER VAPOR WITH TWO SUN REFLECTANCE CHANNELS OF FY-1C SATELLITE

Remote sensing of the total column perceptible water vapor with the imaging spectrometer on the FY-1C polar orbiting satellite is realized based on the algorithm suggested by R. Frouin et al. (1990). With the two sun reflectance channels (a water absorption channel and a window channel), the total column perceptible water vapor is derived. The water absorption channel is at the wavelength of 0.90 to 0.965μm, and the window channel at 0.84 to 0.89μm. The basic formula used is: In the formula, r, the ratio of observation values between the water absorption channel and the window channel, is known. At the locations around radiosonde stations, the total water vapor amount along the observation path is also known. Coefficients A and B can be derived by means of the statistic method. At other locations far from radio sonde stations, m is calculated with coefficients A and B. Factors affecting A are the atmospheric profiles of temperature, pressure and humidity and the channel response function of the imaging spectrometer. The factor affecting B is the surface reflectance. These factors are time-and location-related. Statistic calculation is performed respectively at different time periods and locations. The possible errors that otherwise may be introduced from the incorrect navigation of the images are limited by the quality control measure. Reality examination with independent radiosonde samples shows that the bias is about 15% to 20%, and the correlation coeffecient is above 90%.